数据发送到活动的接口崩溃
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【中文标题】数据发送到活动的接口崩溃【英文标题】：Crash on Interface on data send to activity 【发布时间】：2017-08-16 21:31:45 【问题描述】：我有一个将执行 asynctask 的主要活动，然后使用接口将数据发送回活动，如下面的代码所示
主要活动
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_profile_scroll);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
String type = "getProfile";
SharedPreferences pref = getApplicationContext().getSharedPreferences("MyPref", 0); // 0 - for private mode
SharedPreferences.Editor editor = pref.edit();
String username = pref.getString("username", null);
RetrieveData retrieveData = new RetrieveData(this);
retrieveData.execute(type,username);
public void sendData(String response)
// TODO Auto-generated method stub
String name="";
String age="";
String gender = "";
String id = "";
try
JSONObject jsonObject = new JSONObject(response);
JSONArray result = jsonObject.getJSONArray("result");
JSONObject collegeData = result.getJSONObject(0);
ImageView imageView = (ImageView) findViewById(R.id.imageView2);
name = collegeData.getString("name");
age = collegeData.getString("age");
gender = collegeData.getString("gender");
id = collegeData.getString("id");
EditText MyName = (EditText) findViewById(R.id.editText14);
MyName.setText(name);
EditText MyAge = (EditText) findViewById(R.id.editText21);
MyAge.setText(age);
EditText MyGender = (EditText) findViewById(R.id.editText22);
MyGender.setText(gender);
Picasso.with(this).load("http://192.168.12.252/"+id+"/profile.png").memoryPolicy(MemoryPolicy.NO_CACHE).networkPolicy(NetworkPolicy.NO_CACHE).into(imageView);
catch (JSONException e)
e.printStackTrace();
异步任务
public class RetrieveData extends AsyncTask<String,Void,String>
Context context;
RetrieveData(Context ctx)
context = ctx;
private OnDataSendToActivity dataSendToActivity;
public RetrieveData(View.OnClickListener activity)
dataSendToActivity = (OnDataSendToActivity)activity;
@Override
protected String doInBackground(String... params)
String profile_url = "http://192.168.12.252/getprofile.php";
String image_url = "http://192.168.12.252/imagelist.php";
String type = params[0];
if(type.equals("getProfile"))
try
String user_name = params[1];
URL url = new URL(profile_url);
HttpURLConnection httpURLConnection = null;
httpURLConnection = (HttpURLConnection)url.openConnection();
httpURLConnection.setRequestMethod("POST");
httpURLConnection.setDoOutput(true);
httpURLConnection.setDoInput(true);
httpURLConnection.setDoOutput(true);
httpURLConnection.setDoInput(true);
OutputStream outputStream = httpURLConnection.getOutputStream();
BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8"));
String post_data = URLEncoder.encode("user_name", "UTF-8")+"="+URLEncoder.encode(user_name, "UTF-8");
bufferedWriter.write(post_data);
bufferedWriter.flush();
bufferedWriter.close();
outputStream.close();
InputStream inputStream = httpURLConnection.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream,"iso-8859-1"));
String result = null;
result = bufferedReader.readLine();
bufferedReader.close();
inputStream.close();
httpURLConnection.disconnect();
return result;
catch (IOException e)
e.printStackTrace();
else if(type.equals("getProfileImages"))
try
String user_name = params[1];
URL url = new URL(image_url);
HttpURLConnection httpURLConnection = null;
httpURLConnection = (HttpURLConnection)url.openConnection();
httpURLConnection.setRequestMethod("POST");
httpURLConnection.setDoOutput(true);
httpURLConnection.setDoInput(true);
httpURLConnection.setDoOutput(true);
httpURLConnection.setDoInput(true);
OutputStream outputStream = httpURLConnection.getOutputStream();
BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8"));
String post_data = URLEncoder.encode("Image", "UTF-8")+"="+URLEncoder.encode("Image", "UTF-8")+"&"+URLEncoder.encode("user_name", "UTF-8")+"="+URLEncoder.encode(user_name, "UTF-8");
bufferedWriter.write(post_data);
bufferedWriter.flush();
bufferedWriter.close();
outputStream.close();
InputStream inputStream = httpURLConnection.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream,"iso-8859-1"));
String result = null;
result = bufferedReader.readLine();
bufferedReader.close();
inputStream.close();
httpURLConnection.disconnect();
return result;
catch (IOException e)
e.printStackTrace();
return null;
@Override
protected void onPostExecute(String result)
super.onPostExecute(result);
dataSendToActivity.sendData(result);
界面
public interface OnDataSendToActivity
void sendData(String str);
当我执行代码时，它在这一行崩溃
dataSendToActivity.sendData(result);
android 监视器中的错误如下所示，我不明白是什么问题
--------- beginning of crash
03-24 04:12:42.518 20964-20964/com.example.lenovo.maidfriends E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.lenovo.maidfriends, PID: 20964
java.lang.NullPointerException: Attempt to invoke interface method 'void com.example.lenovo.maidfriends.OnDataSendToActivity.sendData(java.lang.String)' on a null object reference
at com.example.lenovo.maidfriends.RetrieveData.onPostExecute(RetrieveData.java:119)
at com.example.lenovo.maidfriends.RetrieveData.onPostExecute(RetrieveData.java:33)
at android.os.AsyncTask.finish(AsyncTask.java:667)
at android.os.AsyncTask.-wrap1(AsyncTask.java)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:684)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
我假设它说，结果中没有任何价值，但事实并非如此，结果中有一些东西。
谁能告诉我怎么了？
【问题讨论】：
你有没有初始化 dataSendToActivity 变量。 @santoshgore 你的意思是在异步任务中？我已经编辑了代码，你能帮我再看一遍吗 你的 sendMyData() 方法在哪里？当你调用 sendMyData 时，你调用的对象为空。 @santoshgore 抱歉我贴错了，请再看一下我的错误信息 好的。 dataSendToActivity 为空。所以请验证是否调用了 RetrieveData 构造函数？因为您正在构造函数中设置 dataSendToActivity 的值。 【参考方案1】：您没有覆盖 Main Activity 中的 RetrieveData 函数。您只是在创建一个具有相同名称的新函数。
而不是将 Asynctask 称为：
RetrieveData retrieveData = new RetrieveData(this);
使用以下代码：
RetrieveData retrieveData = new RetrieveData(new RetrieveData()
public void sendData(String response)
// TODO Auto-generated method stub
String name="";
String age="";
String gender = "";
String id = "";
try
JSONObject jsonObject = new JSONObject(response);
JSONArray result = jsonObject.getJSONArray("result");
JSONObject collegeData = result.getJSONObject(0);
ImageView imageView = (ImageView) findViewById(R.id.imageView2);
name = collegeData.getString("name");
age = collegeData.getString("age");
gender = collegeData.getString("gender");
id = collegeData.getString("id");
EditText MyName = (EditText) findViewById(R.id.editText14);
MyName.setText(name);`enter code here`
EditText MyAge = (EditText) findViewById(R.id.editText21);
MyAge.setText(age);
EditText MyGender = (EditText) findViewById(R.id.editText22);
MyGender.setText(gender);
Picasso.with(this).load("http://192.168.12.252/"+id+"/profile.png").memoryPolicy(MemoryPolicy.NO_CACHE).networkPolicy(NetworkPolicy.NO_CACHE).into(imageView);
catch (JSONException e)
e.printStackTrace();
);
移除 Main Activity 的 sendData()
同样在 RetrieveData 类中，替换以下代码：
public RetrieveData(View.OnClickListener activity)
dataSendToActivity = (OnDataSendToActivity)activity;
与：
public RetrieveData(OnDataSendToActivity activity)
dataSendToActivity = activity;
如果您遇到任何问题，请告诉我。
【讨论】：
【参考方案2】：从onPostExecute 调用sendData() 很简单：
MainActivity ma=new MainActivity();
ma.sendData(result);
【讨论】：
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